Caesar Cipher Decoder
Result
Note: the Caesar cipher is a puzzle cipher from ancient Rome. It is not real security. Anyone can try all 25 shifts in seconds, so never use it to protect private or important information.
What is Caesar Cipher Decoder?
Caesar Cipher Decoder encodes and decodes text with the classic Caesar shift cipher, where every letter moves a fixed number of places along the alphabet. Pick any shift from 1 to 25, use ROT13 with one click, or let the brute force table try all 25 shifts at once and highlight the one that looks most like English. Everything runs in your browser and is free with no signup.
How to use
- Paste your cipher text into the input box, or type a plain message to encode.
- Choose Decode to read a message, or Encode to write one.
- Set the shift with the slider, or press ROT13 for a shift of 13.
- If you do not know the shift, read the brute force table and pick the row that reads as English.
Features
- Caesar cipher translator: encode and decode with any shift from 1 to 25.
- One-click ROT13 mode (shift 13).
- Caesar shift decoder: brute force table shows all 25 shifts with the best match highlighted.
- Letter case is preserved, and numbers and punctuation are left alone.
- Runs in your browser, nothing is uploaded.
- Free, private, and no signup required.
Frequently asked questions
What is a Caesar cipher?
It is a simple substitution cipher named after Julius Caesar. Each letter is shifted a fixed number of places, so with a shift of 3, A becomes D, B becomes E, and so on.
How do I use this caesar decoder without knowing the shift?
Use the brute force table below the tool. It decodes your text with all 25 shifts and scores each result by how closely its letter frequencies match English. The lowest score is usually the right answer.
What is a ROT13 decoder?
A ROT13 decoder is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying it twice returns the original text, so the same operation encodes and decodes.
Is the Caesar cipher secure?
No. It is a puzzle cipher with only 25 possible shifts, so anyone can break it in seconds by trying them all. Never use it to protect private or important information.
Does it change numbers and punctuation?
No. Only letters A to Z are shifted. Numbers, punctuation, spaces and line breaks stay exactly as they are.
Is this tool free?
Yes, it is free with no signup and no limits.